Heavy electrical cables are commonly used in the mining industry for powering equipment, such as shovels, drills and the like. Such equipment may operate using a medium voltage electrical service, which may range from 8 kV to 35 kV. As the needs for different equipment and/or equipment locations may change, the configuration of the electrical cables may be reconfigured by adding, removing and/or moving the electrical cables. The cables may be electrically coupled using cable couplers or connectors that may be used to accomplish the changes in electrical power delivery to the equipment.
Mining couplers are adapted from other electrical market products. However, the mining industry has unique requirements, such as quick and reliable connect and disconnect, high environmental contamination and normal operation near the rated current/power levels. These requirements may differ from many electric utility applications such as underground residential distribution (URD). For example, electric utility market models of “plug and play” designs for applications such as underground residential distribution generally do not see full current loading, are in relatively clean environments and the mechanical duty requirements are relatively low compared to mining.
In contrast with low voltage applications, the connectors are characterized as being inseparable in that the electrical service must be de-energized during disconnection to avoid injury to personnel. Disconnecting electrically energized connectors can and has caused serious personal injury, which, in some cases has resulted in death. In this regard, techniques to avoid disconnecting energized (i.e., “live”) connectors have been developed.
One conventional technique includes providing a test point on the connector that is capacitively charged by the electric field between the primary conductor and the grounded outer layer. This test point develops a voltage that may be tested using an elongated insulated test probe, referred to as a “hot stick”, and metering equipment, to determine if the test point has a voltage. This technique has the disadvantage of requiring personnel to carry and maintain equipment to determine that the connector is not energized.
Another conventional technique for preventing an energized connector from being disconnected includes one or more special ground contacts that are in the connector and that conductively disengage before the primary voltage line is disconnected. These special ground contacts may control one or more relays at control equipment locations to disconnect the electrical power to the connector before the primary voltage line is disconnected. However, these systems can be adjusted in the field and rendered inoperable in response to nuisance trips that may reduce production activities. Accordingly, an additional level of personnel safety in disconnecting connectors is needed.